1. Field of the Invention
The present invention relates to a reduction gear for reducing a high rotational spped of an electric motor, or the like, to a predetermined lower rotational speed. The invention particularly relates to the reduction in play due to back-lash in gears in such a reduction gear.
2. Background of the Invention
In the conventional reduction gears, input rotation is generally reduced by means of a gear train. In such a reduction gear, however, back-lash is inevitably caused in gearing of gears so that play is caused corresponding to the back-lash.
On the other hand, in a reduction gear of a harmonic drive system which has come into wide use recently, back-lash is almost eliminated. However, in the structure of a harmonic drive system, the difference in teeth number between a flexible spline structure and a circular spline structure is limited to only about 1 or 2 and therefore such a reduction gear can be used only in the case where there is a high reduction ratio of at least 1:50-1:60.